Polyolefin oil resistant film using polar polymer

ABSTRACT

A biaxially oriented polyolefin multilayer film having a skin layer made of a blend of a polar polymer and a non-polar polymer is disclosed. The film has substantially no inorganic fillers and yet shows no visible distortion after exposure to food products such as potato chips.

RELATED APPLICATIONS

[0001] This application claims priority from Provisional ApplicationSerial No. 60/315,672 filed Aug. 30, 2001, entitled the same as above,the entire disclosure of which is hereby incorporated herein byreference.

FIELD OF INVENTION

[0002] The invention relates to polyolefinic multilayer film comprisinga core layer of polypropylene and at least one outer layer. Morespecifically, the invention relates to a biaxially orientedpolypropylene film that does not distort in the presence of food oils.

BACKGROUND OF INVENTION

[0003] Biaxially oriented polypropylene film laminations are commonlyused in the snack food packaging industry. In particular, potato chippackaging is a very large volume application.

[0004] In the case of potato chip packaging, oils such as cottonseedoil, corn oil, and soybean oil are present on the potato chip surface.Some of this oil on the potato chip surface transfers to the package'sinternal surfaces. Similarly, other types of baked food snack productsalso have oils that are known to swell the polypropylene. Since thesefood oils are non-polar, the polypropylene film absorbs them quitereadily, particularly at elevated temperatures. This absorption of foodoils by the film gives a distorted appearance to the entire package bycausing dimpling in the film.

[0005] This surface distortion effectively destroys the surface gloss ofthe package and gives the appearance that the package has beenmishandled. This distortion is undesirable to snack food manufacturers,as they would like to represent the product as being fresh or new to theshelf.

[0006] Oriented polypropylene films currently available on the markethave attempted to address this issue in two ways. First, by stiffeningthe film such that the distortions are not so visible to the human eye.Second, by preventing the migration of the food oils into thepolypropylene layer(s) of the film.

[0007] The stiffening of the film is typically done by adding inorganicfillers such as calcium carbonate, titanium dioxide, etc., to the corelayer of the film. The addition of fillers not only provide increasedstiffness but could also provide opacity, e.g., by creating voids usingCaCO₃, and whiteness, e.g., by using TiO₂. See, U.S. Pat. Nos. 4,303,708(Gebhardt), 4,377,616 (Ashcraft), 4,632,869 (Park), 4,652,489 (Crass),5,134,173 (Joesten), and 6,048,608 (Peet). The common features of thesepatents is that they use fillers in a core layer for creating opacity inthe film and have a void-free layer on the surface of the film thatwould contact the food products.

[0008] Typically, for preventing migration of the food oils to thepolypropylene layer(s) of the film, a metallized layer such as analuminum layer is applied to the inside the film in contact with thefood products. The oil does not penetrate though an intact aluminumlayer. However, the problems of applying the metallized layer on theinside of the film are the following. First, the metallized layer tendsfor form cracks through which the oils leak into the polypropylenelayer(s) of the film. Second, it is preferred to have the metallizedlayer on the side of the film that will be the outside surface of thefood package. This is because the metallized layer provides a glossybackground to the images printed on the surface of the food package.

[0009] The idea behind the prior art films was the following. If one canprevent migration of the oils from the food products into the film usinga solid, void-free layer on the film surface that would be in contactwith the food products, then one should be able to minimize migration ofoils into the film. Thereby, one can prevent distortion of the film. Ifdistortion is still visible, the prior art films attempted to minimizedistortion by stiffening the films by adding fillers to the core layer.

[0010] The approach utilized by the prior art films discussed above hasthe following impacts. It generally does not prevent migration of theoils into the core layer, but the distortion is suppressed by stiffeningthe film and increasing the thickness of the film. Stiffening the filmmakes the film heavier and less flexible while increasing the filmthickness increases the cost of the film. Therefore, it is the objectiveof this invention to provide an economical solution to this packagedistortion problem caused by the oils of the food product beingpackaged.

SUMMARY OF THE INVENTION

[0011] This invention provides a film that does not distort in thepresence of food oils, particularly at elevated temperature conditions.This invention further maintains the necessary properties of the filmincluding oxygen barrier, moisture barrier, cold seal adhesion, and heatseal performance. Achieving these objectives will result in a packagewith very good surface aesthetics, excellent heat seal or cold sealadhesion performance, and exceptional barrier performance.

[0012] As explained above, the prior art structures use fillers to makethe film stiff and opaque. In addition, the prior art structures use avoid-free layer on the film surface contacting the food products toprevent migration of the food oils into the film.

[0013] The applicants of this invention have arrived at a novel approachthan that adopted by the prior art structures to solve the problem ofdistortion. Applicants have found that blending a certain quantity of apolar polymer in a non-polar polyolefin produces a film having excellentoil resistance that exhibits substantially no distortion. Applicantshave successfully produced such a film structure that is capable ofmaking a finished package product having the followingcharacteristics: 1) strong seals, 2) excellent barrier, 3) excellentlamination bond strength, 4) excellent print quality, and 5) excellentgloss or surface aesthetics.

[0014] Applicants have also determined that increasing the thickness ofthe lamination can reduce this distortion. Thus, increasing thelamination thickness lends additional structural support to thelamination and reduces the distortion of the entire package. However,increasing the thickness of the lamination is uneconomical sinceconsuming more raw materials is always considerably more expensive.

[0015] As will be realized, this invention is capable of other anddifferent embodiments, and its details are capable of modifications invarious obvious respects, all without departing from this invention.Accordingly, the description is to be regarded as illustrative in natureand not as restrictive.

DETAILED DESCRIPTION OF THE INVENTION

[0016] This invention provides a polyolefin film preferably having atleast two layers, including a first skin layer, which is in directcontact with the packaged product. This skin layer could be functionalsuch as a heat seal layer or a cold seal adhesion layer and may alsocontain void initiating solid particles. A core layer, adjacent to thepolyolefin skin layer, may also contain void initiating solid particles.A second polymeric skin layer may also be incorporated on the oppositeside of the core layer from the first skin layer. This second polymericlayer may function as a layer for metallization, printing, adhesivelamination, extrusion lamination and coatings. More particularlypreferred is a layer for metallization.

[0017] The skin layer is made of a blend of a non-polar polyolefinpolymer and a polar polymer. The skin layer can function as a heat-seallayer or a layer for cold seal adhesion. The term heat seal is definedas sealing upon the onset of heat. For a package to cold seal, a coldseal cohesive must be pattern applied by a rotogravure coating processto the cold-seal adhesion skin layer. The term cold seal is defined assealing a product at room temperature with the application of onlypressure.

[0018] The term blend refers to a material made from two or morepolymers mixed together. The blend could further include additionalsubstances such as monomers, oligomers, additives, compatibilizers, etc.A polymer is a molecule made up by the repetition of some simpler unit,the “mer” or monomer.

[0019] The blend could be a miscible blend or an immiscible blend. Ingeneral, a miscible blend of two polymers forms a substantiallyhomogeneous mixture so as to render the components of the blendsindistinguishable from one another. A miscible blend generally hasproperties somewhere between those of the two unblended polymers. Forexample, the glass transition temperature, or T_(g), of a miscible blendof polymer A and polymer B will be a value depending on the ratio ofpolymer A to polymer B in the blend.

[0020] An immiscible blend is a phase-separated mixture of two or morepolymers. But strangely enough, the phase-separated materials often turnout to be rather unique and useful. One unusual property of immiscibleblends is that one made from two polymers has two glass transitiontemperatures or T_(g)s. Since the two components of the blend are phaseseparated, each component retains its separate T_(g). One can measurethe T_(g) of a blend to find out if it is miscible or immiscible. If twoT_(g)s are found, then the blend is immiscible. If only one T_(g) isobserved, then the blend is likely to be miscible.

[0021] This invention is not limited to a specific mechanism by whichthe blend of the polar and non-polar polymers provides improved oilresistance. However, one possible mechanism that could explain theimproved oil resistance of the claimed film is that the polar polymer ofthe blended skin layer would migrate to the outside surface of the skinlayer exposed to the environment, which is generally the inside of afood package. The polar polymer would migrate predominantly because ofthe polarity difference between the two polymers. In addition, the useof a preferred low viscosity or high melt index polar polymer would alsofacilitate the polar polymer to easily migrate to the surface of thefilm upon which the food oil resides. The polar polymer acts as abarrier to the food oils that come into physical contact with thislayer, since non-polar oils have difficulty penetrating or swellingpolar polymers.

[0022] In one embodiment, the present invention is a multi-layersealable polyolefin film that provides excellent distortion resistanceto food oils. Specifically, the film is a biaxially orientedpolypropylene multi-layer film comprising a first surface layer (whichwould contact food stuff when the multi-layer film is used in foodpackaging) containing a blend of a non-polar polyolefin polymer and apolar polymer. Additional layers could include a core layer comprising apolypropylene polymer and second surface layer on the side. The corelayer could be between the first and second surface layers. The firstand/or second surface layers, preferably of polyolefin, could be furthertreated by a discharge surface treatment method that imparts a highsurface energy.

[0023] The core layer can be any polyolefin polymer that can beuniaxially or biaxially oriented. Such polymers include but are notlimited to: isotactic polypropylene homopolymer, syndiotacticpolypropylene homopolymer, metallocene catalyzed isotactic polypropylenehomopolymer, metallocene catalyzed syndiotactic polypropylene,ethylene-propylene random copolymer, butene-propylene random copolymer,high density polyethylene, low density polyethylene, linear low densitypolyethylene and blends thereof. Most preferred is a core layer of anisotactic polypropylene homopolymer resin. The isotactic polypropyleneresin can be defined as having a melt flow in the range of 1-9 g/10 min.More particularly preferred is a melt flow rate in the range of 1-5 g/10min. Most particularly preferred is a melt flow rate in the range of 1-3g/10 min.

[0024] The core layer can be surface treated with either a standardcorona treatment, flame treatment, atmospheric plasma, or a specialcorona treatment utilizing a mixed gas environment of nitrogen andcarbon dioxide. Most preferred is a surface treatment by coronautilizing a mixed gas environment of nitrogen and carbon dioxide. Thiscore layer can then be directly metallized, printed, coated, adhesivelaminated, or extrusion laminated. Most particularly preferred ismetallization of the core layer.

[0025] The skin layer could be a cold seal adhesion layer. The cold sealadhesion layer can be composed of any of the following and blendsthereof: an isotactic polypropylene homopolymer, syndiotacticpolypropylene homopolymer, metallocene catalyzed isotactic polypropylenehomopolymer, metallocene catalyzed syndiotactic polypropylenehomopolymer, ethylene-propylene random copolymer, butene-propylenerandom copolymer, ethylene-propylene-butene-1 terpolymer, low densitypolyethylene, linear low density polyethylene, very low densitypolyethylene, metallocene catalyzed polyethylene, metallocene catalyzedpolyethylene copolymers, ethylene-methacrylate copolymers,ethylene-vinyl acetate copolymers, and ionomer resins.

[0026] This cold seal adhesion layer can be surface treated with eithera standard corona treatment, flame treatment, atmospheric plasma, or aspecial corona treatment utilizing a mixed gas environment of nitrogenand carbon dioxide. Most particularly preferred is corona treatment.

[0027] The skin layer could be a heat sealable layer. The heat seallayer can be composed of any of the following and blends thereof: anethylene-propylene random copolymer, ethylene-butene-1 copolymer,ethylene-propylene-butene-1 terpolymer, propylene-butene copolymer, lowdensity polyethylene, linear low density polyethylene, very low densitypolyethylene, metallocene catalyzed polyethylene plastomer, metallocenecatalyzed polyethylene, metallocene catalyzed polyethylene copolymers,ethylene-methacrylate copolymer, ethylene-vinyl acetate copolymer andionomer resin.

[0028] One aspect of this invention is the use of a polar polymer in theskin layer. When blended with the non-polar polyolefin polymer, thepolar polymer is driven to the outside surface of the skin layer. Thispolar outermost layer will effectively act as a barrier to the food oilsand thus prohibit the oils from swelling and distorting thepolypropylene film.

[0029] The desirable attributes of the polar polymer include thepolarity, melt flow rate, and melting temperature. In particular, themelting temperature range is from 76° C. to 158° C.; the melt flow rateis in the range from 4.5 to 14 g/10 min; and the density is in the rangefrom 0.95 to 1.19 g/cc.

[0030] Among the polymers that meet these criteria are polyethyleneionomer resins, modified ethylene acrylate polymers, ethylenemethacrylic acid copolymer, and amorphous nylon called Surlyn®, Appeel®,Elvaloy®, and Selar PA®, respectively, from DuPont, ethylene acrylicacid copolymers called Primacor® from Dow Chemical Company, ethylenevinyl alcohol copolymer called Eval® from Evalca and ethylene acidterpolymer called Escor® from ExxonMobil.

[0031] Surlyn® is a random copolymer of poly(ethylene-co-methacrylicacid) (EMAA). The incorporation of methacrylic acid is typically low(less than 15 mole percent). Some or all of the methacrylic acid unitscould be neutralized with a suitable cation, commonly Na⁺ or Zn⁺².Surlyn® is produced through the co-polymerization of ethylene andmethacrylic acid via a high pressure free radical reaction, similar tothat for the production of low density polyethylene. The methacrylicacid monomer is more reactive with itself than with ethylene. This leadsto a higher reactivity ratio, around four, for methacrylic acid, andcould give a blocky incorporation of methacrylic acid along the polymerchain. However, by polymerizing under elevated heat and pressure thereactivity ratios are driven toward one, thus promoting a randomincorporation of the co-monomers. The neutralization of the methacrylicacid units can be done through the addition an appropriate base insolution, or in the melt mixing of base and copolymer.

[0032] The inclusion of a few mole percent ionic groups along thebackbone has a tremendous effect upon the morphology and properties ofSurlyn.® Poly(ethylene-co-methacrylic acid) ionomers typically show anincreased melt viscosity, toughness, clarity, and adhesion. Theincreased clarity, a desirable property in packaging applications, isdue to the reduction of crystalline content of the copolymer. Thepresence of the methacrylic acid units and the neutralized carboxylateanion/cation pairs provides sites for ionic interaction. Hydrogenbonding between carboxylic acid moieties could form dimers. Interactionsbetween ion pairs, and the non-polar nature of the backbone, could causethe ions to aggregate together. At low mole percent incorporation ofmethacrylic acid, or low percent neutralization, the ion pairs willexist as isolated polar groups in the bulk of Surlyn.® However, above acertain critical ionic concentration, the ion pairs will assemble intolarger groups. The end result is the formation of an ion rich phasewithin the bulk of the polymer. The assembled ionic aggregates act asthermally reversible cross-links, greatly modifying the viscoelasticproperties of the resulting polymer. These aggregations of ions,typically on the order of a few nanometers in size, serve as scatteringcenters for small angle x-ray scattering (SAXS). A typical SAXS profileof Suryln® shows low-density polyethylene, poly(ethylene-co-methacrylicacid) and Na+ neutralized poly(ethylene-co-methacrylic acid). In the Na+neutralized ionomer profile one sees a small angle peak, due to thepresence of the ionic aggregates. In general, the aggregation of ionsdepends on a variety of factors, such as strength of ionic interaction,steric considerations of packing the ionic pairs, and conformationalmobility of the polymer backbone.

[0033] Surlyn® is a semi-crystalline polymer in both the acid andneutralized forms. The presence of the methacrylic acid units limits theability of the copolymer to pack in a crystalline lattice, and the ionicinteractions slow the formation of spherulites.

[0034] The Elvaloy® resin family includes eight ethylene methylacrylates (EMAs), four ethylene ethyl acrylates (EEAs) and six ethylenebutyl acrylates (EBAs). They range in melt flow from 0.4 to 9.0 g/10min, and acrylate content runs from 7% to 27%.

[0035] The Elvaloy® resins have a greater thermal stability than EVAs.The Elvaloy® resins have higher melting points and melt strength thansimilar acrylate copolymers. A food-grade, high-comonomer EMA resin,Elvaloy 1224 AC (24% acrylate) could preferably be used as a polarpolymer in the present invention.

[0036] Selar® PA amorphous nylon barrier resins provide unique oxygenbarrier properties when wet or chilled, making the resins a good choicefor flavorsensitive refrigerated foods and beverages. In bottles, jarsand other rigid structures, Selar® PA offers the crystal clarity ofglass, but with lower weight and better impact resistance. Selar® PA canbe blended with nylon 6 and with EVOH to provide certain property andprocessing advantages.

[0037] In a Primacor® resin, acrylic acid is randomly incorporated withethylene. The carboxyl groups are free to form bonds and to interactwith any polar substrate such as metals, glass, cellulosics, andpolyamides. Carboxyl groups on adjacent chains can hydrogen bond witheach other. This produces toughness even at relatively low molecularweights. Additionally, the polymer can be cross-linked through thebackbone and the acid functionality, allowing further improvements intoughness. The bulky carboxyl groups inhibit the ability of the polymerto crystallize. This improves optical clarity and reduces both meltingand softening points.

[0038] It is preferred that the polar polymer has a low viscosity to beable to move to the surface effectively during extrusion. The film istypically made by in a biaxially oriented polypropylene process. Thisprocessing is very heat sensitive and as such requires that the polarpolymer have a relatively high melting temperature. If the skin layer isa sealant layer, then it is preferable that the polar polymer has arelatively low melting temperature to maintain seal properties.Therefore, a balance between processability and performance is requiredto achieve the end product.

[0039] While low viscosity of the polar polymer is preferred asexplained above, yet very low viscosity is not preferred because themiscibility between a very low viscosity polar polymer and the non-polarpolymer in the skin layer, preferably a polyolefin, can be poor. Also,very low viscosity polar polymer could result in poor molecularentanglement between the molecules of the polar polymer and thenon-polar polymer in the skin layer.

[0040] The viscosity of the polar and non-polar polymers is a functionof the molecular weight. Preferably, the number average molecular weight(Mn) should be greater than about 5,000. More preferably, Mn should begreater than about 20,000. The polar and/or non-polar polymers couldhave Mn in the range of about 10,000 to about 150,000, more preferablyin the range of about 25,000 to about 100,000, and most preferably inthe range of 50,000 to 75,000. The polar and/or non-polar polymers couldhave a polydispersity (Mw/Mn), where Mw is weight average molecularweight, in the range of about 1.1 to about 15, preferably in the rangeof about 1.5 to about 10, more preferably in the range of about 2 toabout 6, and most preferably in the range of about 3 to about 5.

[0041] The amount of the polar polymer in the skin layer could be in therange of about 1 to about 50 percent by weight. Preferably, the amountof the polar polymer in the skin layer should be in the range of about 5to about 25 weight percent. Most preferably, the amount of the polarpolymer in the skin layer should be in the range of about 10 to 20weight percent. The amount of the polar polymer should be at least asmuch as would be required to form a layer of polar molecules on the skinlayer.

EXAMPLES

[0042] A 65 gauge biaxially oriented polypropylene (BOPP) film wasmanufactured on a 1.5-meter wide BOPP production line. The skin layerwas measured at 6 gauge units. The skin layer used anethylene-butene-propylene terpolymer at a melt flow rate of 9.5 g/10 minas measured by ASTM D1238. A certain amount by weight of the polarpolymer was added to the skin layer as shown in Table 1. Isotacticpolypropylene resin was used in the core layer. The melt flow rate ofthe core isotactic polypropylene homopolymer was 1.6 g/10 min.

[0043] The films were metallized in a Shimadzu bell jar metallizer thatevaporated aluminum on the core side of the film. Potato chips were thencrushed into small pieces. Ten grams of the crushed potato chips wereweighed and placed in a 9.6 in² surface area on the skin layer side ofthe film. The samples were next placed in a convection oven at 115° C.for 3 and 6 hours respectively. The crushed chips and oil were thencleaned from the surface with isopropyl alcohol. The samples wereevaluated qualitatively for film distortion by seeing the amount ofdimpling occurring in the film. A rating of 5 was given for the worstdistortion, a rating of 0 was given for a sample that has no distortion.Thus, the data in Table 1 is based on this relative ranking system.TABLE 1 Effect of Polar Resin in Skin Layer on Oil Resistance of OPPFilms. Oil Dimpling Rate after, hrs Sample # Polar Resins % 1 2 3 6 1Control, None N/A 1 1 2 3 2 EMA 10 1 2 2 2 Elcalay AC 1820 3 EMA 20 0.51 1 2 Elcalay AC 1820 4 EA Terpolymer 10 0.5 0.5 1 2 AT-320 5 EATerpolymer 20 0.5 0.5 0.5 1 AT-320 6 EAA 10 0.5 0.5 0.5 1 Primacor 34407 Ionomer 10 1 1 1 2 Surlyn 1702

[0044] Sample 1 (Control) contains no polar polymer in the skin layer.The skin layer of Samples 1-7 contains ethylene-propylene-butylene (EPB)terpolymer as the non-polar polymer. A non-polar polymer such as EPBalso acts as a sealant.

[0045] Table 1 shows that the distortion in the Control film was badafter testing for distortion. The distortions in the films of Samples 5and 6 were substantially non-existent after testing for distortion. Bycomparing the films of Samples 5 and 6, it was seen that just 10-weightpercent ethylene acrylic acid (EEA) in the skin layer provides oildimple rating of 1. On the other hand, the same rating was obtained by20-weight percent of ethylene acid (EA) terpolymer used in the skinlayer. This is possibly because EEA in Sample 6 could more effectivelymigrate to the surface of the skin layer than EA in Sample 5.

[0046] By comparing the films of Samples 2 and 3, in which the amount ofthe polar polymer (EMA) was 10 and 20 weight percent, respectively, inthe skin layer, one notices the following. First, by increasing theamount of polar polymer in the skin layer, it is possible to delay theonset of dimpling. However, it appears that the maximum oil dimple rateis controlled by the presence of the type of polar polymer on thesurface of the skin layer, not so much by the amount of the polarpolymer present in the skin layer.

[0047] The above description is presented to enable a person skilled inthe art to make and use the invention, and is provided in the context ofa particular application and its requirements. Various modifications tothe preferred embodiments will be readily apparent to those skilled inthe art, and the generic principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the invention. Thus, this invention is not intended to belimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein.

[0048] This application discloses several numerical range limitations.Persons skilled in the art would recognize that the numerical rangesdisclosed inherently support any range within the disclosed numericalranges even though a precise range limitation is not stated verbatim inthe specification because this invention can be practiced throughout thedisclosed numerical ranges. A holding to the contrary would “let formtriumph over substance” and allow the written description requirement toeviscerate claims that might be narrowed during prosecution simplybecause the applicants broadly disclose in this application but thenmight narrow their claims during prosecution. Finally, the entiredisclosure of the priority documents, patents and publications referredin this application are hereby incorporated herein by reference.

1. A biaxially oriented polyolefin multilayer film comprising a skinlayer comprising a blend of a polar polymer and a non-polar polymer, theskin layer having a surface exposed to an environment surrounding thefilm and being a single layer, wherein a number average molecular weightof the polar polymer is greater than about 5,000, an amount of the polarpolymer in the skin layer is in the range from about 1 to about 50weight percent based on the total weight of the skin layer and thenon-polar polymer comprises polyolefin.
 2. The film of claim 1, whereinthe polar polymer is on a surface of the skin layer exposed to anenvironment.
 3. The film of claim 1, wherein the polar polymer and thenon-polar polymer are immiscible.
 4. The film of claim 1, wherein thenumber average molecular weight of the polar polymer is greater thanabout 20,000.
 5. The film of claim 1, wherein an amount of the polarpolymer in the skin layer is in the range from about 5 to about 40weight percent based on the total weight of the skin layer.
 6. The filmof claim 1, wherein an amount of the polar polymer in the skin layer isin the range from about 10 to about 20 weight percent based on the totalweight of the skin layer.
 7. The film of claim 1, wherein the skin layerfurther comprises a compatibilizer for compatibilizing the polar polymerand the non-polar polymer.
 8. The film of claim 1, wherein an amount ofthe non-polar polymer in the skin layer is about 50 weight percent ormore based on the total weight of the skin layer.
 9. The film of claim1, wherein the non-polar polymer comprises polypropylene.
 10. The filmof claim 1, wherein the skin layer is a cold seal adhesion layer, a heatsealable layer, or combinations thereof.
 11. The film of claim 10,wherein the cold seal adhesion layer is surface treated with a coronatreatment, a flame treatment, atmospheric plasma, or a corona treatmentutilizing a mixed gas environment of nitrogen and carbon dioxide. 12.The film of claim 10, wherein the cold seal adhesion layer comprises amaterial selected from the group consisting of an isotacticpolypropylene homopolymer, syndiotactic polypropylene homopolymer,metallocene catalyzed isotactic polypropylene homopolymer, metallocenecatalyzed syndiotactic polypropylene homopolymer, ethylene-propylenerandom copolymer, butene-propylene random copolymer,ethylene-propylene-butene-1 terpolymer, low density polyethylene, linearlow density polyethylene, very low density polyethylene, metallocenecatalyzed polyethylene, metallocene catalyzed polyethylene copolymers,ethylene-methacrylate copolymers, ethylene-vinyl acetate copolymers,ionomer resins and combinations thereof.
 13. The film of claim 10,wherein the heat sealable layer comprises a material selected from thegroup consisting of an ethylene-propylene random copolymer,ethylene-butene-1 copolymer, ethylene-propylene-butene-1 terpolymer,propylene-butene copolymer, low density polyethylene, linear low densitypolyethylene, very low density polyethylene, metallocene catalyzedpolyethylene plastomer, metallocene catalyzed polyethylene, metallocenecatalyzed polyethylene copolymers, ethylene-methacrylate copolymer,ethylene-vinyl acetate copolymer, ionomer resin and combinationsthereof.
 14. The film of claim 1, further comprising a core layer. 15.The film of claim 14, wherein the core layer comprises a materialselected from the group consisting of isotactic polypropylenehomopolymer, syndiotactic polypropylene homopolymer, metallocenecatalyzed isotactic polypropylene homopolymer, metallocene catalyzedsyndiotactic polypropylene, ethylene-propylene random copolymer,butene-propylene random copolymer, high density polyethylene, lowdensity polyethylene, linear low density polyethylene and combinationsthereof.
 16. The film of claim 14, wherein the core layer is surfacetreated with a corona treatment, a flame treatment, atmospheric plasma,or a corona treatment utilizing a mixed gas environment of nitrogen andcarbon dioxide.
 17. The film of claim 1, further comprising a metallizedlayer.
 18. The film of claim 17, wherein the metallized layer comprisesaluminum and has an optical density in the range of from about 1.6 toabout 3.5.
 19. The film of claim 1, wherein a thickness of said skinlayer is in a range of about 5% to about 25% of the total thickness ofthe film.
 20. The film of claim 1, wherein a thickness of said skinlayer is in a range of about 10% to about 20% of the total thickness ofthe film.
 21. The film of claim 1, wherein the polar polymer has amelting temperature in a range from about 50° C. to about 145° C.; amelt index in a range from about 2 g/10 min to about 20 g/10 min; and adensity in a range from about 0.91 g/cc to about 0.97 g/cc.
 22. A foodpacking material comprising a biaxially oriented polyolefin multilayerfilm comprising a skin layer comprising a blend of a polar polymer and anon-polar polymer, the skin layer having a surface exposed to anenvironment surrounding the film and being a single layer, wherein anumber average molecular weight of the polar polymer is greater thanabout 5,000, an amount of the polar polymer in the skin layer is in therange from about 1 to about 50 weight percent based on the total weightof the skin layer and the non-polar polymer comprises polyolefin,further wherein a thickness of said skin layer is in a range of about 1%to about 40% of the total thickness of the film.
 23. The food packagingmaterial of claim 22, wherein a thickness of said skin layer is in arange of about 5% to about 25% of the total thickness of the film. 24.The food packaging material of claim 22, wherein a thickness of saidskin layer is in a range of about 10% to about 20% of the totalthickness of the film.
 25. The food packaging material of claim 22,further comprising an adhesive layer.
 26. The food packaging material ofclaim 22 comprising substantially no inorganic fillers.
 27. The foodpackaging material of claim 22, wherein the polar polymer has a meltingtemperature in a range from about 50° C. to about 145° C.; a melt indexin a range from about 2 g/10 min to about 20 g/10 min; and a density ina range from about 0.91 g/cc to about 0.97 g/cc.